The present invention generally relates to optical telecommunications. More specifically, the present invention relates to the optimization of optical fiber dispersion maps using slope-compensating optical fibers.
Light propagating within an optical fiber undergoes chromatic dispersion which causes the light to be delayed within the optical fiber. The specific amount of dispersion that light undergoes varies depending upon the wavelength of the light. The manner in which an optical fiber causes light to undergo chromatic dispersion is typically characterized by two parameters: (1) the dispersion at one specific wavelength, and (2) the dispersion slope. The dispersion slope indicates the extent to which dispersion varies as a function of wavelength.
The dispersion slope of an optical fiber can significantly limit the usable bandwidth for a wavelength-division multiplex (WDM) system, which uses multiple information channels each having their own wavelength of light. Each information channel can accumulate its own amount of dispersion of the transmission link length. For example, in a WDM system having 10 Gb/s data-rate information channels, the information channels can accumulate a large amount of dispersion (e.g., more than ∀ 3000 ps/nm) over long transmission distances, such as transoceanic transmission distances (e.g., 7000-10,000 km). When the accumulated dispersion is too large, the system performance is degraded due to intersymbol interference which in turn limits the system bandwidth.
Dispersion maps are known that attempt to compensate for accumulated dispersion, thereby expanding the usable bandwidth. For example, dispersion maps are known which use dispersion-compensating optical fibers. In one such example, optical fiber segments having dispersions with a similar magnitude, but opposite signs, can be alternatingly connected to define the optical link. In such a known dispersion map, the end-to-end path average dispersion remains low and fiber nonlinearities are suppressed.
Such a known dispersion map, however, suffers shortcomings. For example, the end-to-end path average dispersion varies significantly from wavelength to wavelength over long transmission distances due to the non-matching dispersion slopes of the two alternating optical fibers that define the overall optical link. Thus, a need exists to reduce the end-to-end path average dispersion below a tolerance threshold over a wide range of wavelengths. This need is particularly desirable with the prevalence of WDM systems and with the desire to increase the number of WDM channels.